Half a Million M Dwarf Stars Characterized Using Domain-adapted Spectral Analysis

Abstract We present fundamental atmospheric parameters ( T eff and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mspace width="0.25em"/> <mml:mi>g</mml:mi> </mml:math> ) and metallicities ([M/H]) for 507,513 M dwarf stars using low-resolution spectra ( R ∼ 1800) from LAMOST DR10. By employing Cycle-StarNet, an innovative domain adaptation approach, we successfully bridge the gap between theoretical PHOENIX synthetic spectra and observed LAMOST spectra, enabling parameter measurements even for lower signal-to-noise (S/N) data (S/N &gt; 5). The fitting residual analysis shows a reduction from 2.0 times to 1.68 times the flux uncertainty. Comparing with available literature values, we find systematic offsets and precisions of 12 ± 70 K in T eff , −0.04 ± 0.17 dex in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mspace width="0.25em"/> <mml:mi>g</mml:mi> </mml:math> , and −0.06 ± 0.20 dex in [M/H]. The precision improves for higher-quality spectra (S/N &gt; 50) to 47 K, 0.12 dex, and 0.14 dex respectively. The metallicity consistency between wide binaries shows a scatter of 0.24 dex, improving to 0.15 dex at S/N &gt; 50. We provide a comprehensive catalog including stellar parameters, spectral classifications, activity indicators, and binary/variability flags, establishing a resource for studies of the most numerous stellar population. The complete catalog can be accessed at doi:10.5281/zenodo.14030249.